Semiconductor devices and methods of fabricating the same

2. The method of claim 1, further comprising measuring a sum of thicknesses of the second and third epitaxial layers by using an upper surface of the first epitaxial layer as a reference line.

3. The method of claim 1, wherein the first epitaxial layer comprises silicon carbide and/or silicon germanium.

4. The method of claim 1, wherein a thickness of the second epitaxial layer is from about 1000 Å to about 1500 Å.

5. The method of claim 1, wherein the impurity region has a crystal defect density lower than a crystal defect density of the preliminary impurity region.

6. The method of claim 1, wherein an upper portion of the active fin comprises an undoped semiconductor pattern that is a portion of an undoped semiconductor layer.

9. The method of claim 8, wherein a thickness of the channel region in a vertical direction that is substantially perpendicular to the horizontal direction is about 1.1 times a thickness of one of the pair of source/drain regions in the vertical direction.

10. The method of claim 8, wherein heating the substrate is performed at an ambient temperature of from about 850° C. to about 950° C. and for from about 20 min to about 50 min.

12. The method of claim 8, wherein the impurity region has a crystal defect density lower than a crystal defect density of the preliminary impurity region.

15. The method of claim 14, wherein forming the channel layer comprises forming an undoped semiconductor layer by performing an epitaxial growth process using the second epitaxial layer as a seed layer.

17. The method of claim 14, wherein an upper portion of each of the active fins comprises a portion of the second epitaxial layer and a portion of the channel layer.